How to open popup windows in response to an event in view model

Question

Hi All,

I'm developing a Windows store app using XAML+C#, following MVVM framework.

I have  a login form which taked userid and password and logs into a database. If the login failed, i need to open an exception popup on the same login screen.Let's say login screen's name is homepage.xaml and the view model which contains all the login work flow is loginviewmodel.

Now, if connection to the database fails a message will be sent by the connection service. I need to raise a popup in the view based on the message i see in the viewmodel.

Any help/pointers are greatly appreciated.

Thanks in advance,

Chandra